In the operation of nuclear reactors, it is customary to remove fuel assemblies after their energy has been depleted down to a predetermined level. Upon removal, this spent nuclear fuel is still highly radioactive and produces considerable heat, requiring that great care be taken in its packaging, transporting, and storing. In order to protect the environment from radiation exposure, spent nuclear fuel is first placed in a canister. The loaded canister is then transported and stored in large cylindrical containers called casks. A transfer cask is used to transport spent nuclear fuel from location to location while a storage cask is used to store spent nuclear fuel for a determined period of time.
In a typical nuclear power plant, spent nuclear fuel is loaded into a canister while submerged in a pool of water. The canister is sealed and loaded into a transfer cask while still submerged in the pool. Once loaded with the canister, the transfer cask is used to transport the canister to a receiving cask (i.e., a storage cask or a transport cask). The loaded canister is then transferred from the transfer cask to the receiving cask for either storage or further transport. During transfer from the transfer cask to the receiving cask, it is imperative that the loaded canister is not exposed to the environment.
As a result of this need, the prior method for transferring a loaded canister from a transfer cask to a receiving cask is to raise the transfer cask above the receiving cask and secure the transfer cask atop the receiving cask so that the casks are in a vertically stacked orientation. The transfer cask is adapted so that its bottom can be opened while it remains stacked upon an open receiving cask. Once the bottom of the transfer cask is opened, the loaded canister is lowered from the transfer cask into the receiving cask with a negligible amount of radiation exposure to operations personnel.
Most casks are very large structures and can weigh up to 250,000 lbs. and have a height of 16 ft. or more. As such, stacking a transfer cask atop a receiving cask requires a lot of space a large overhead crane and possibly a restraint system for stabilization. Typically, the transfer of a loaded canister using this stacking method is done inside a 10 C.F.R. 50 structure of a nuclear power plant, which is fully equipped with an overhead crane and radiation containment devices to protect the health and safety of the surrounding communities in the event of a loading mishap. However, numerous nuclear power plants do not possess a 10 C.F.R. 50 qualified staging area that is either large enough to accommodate the stacking of the transfer cask and receiving cask, qualified to support the load of the stacked casks, and/or possesses qualified load handling equipment to make the canister transfer indoors. For such sites, the canister transfer must be completed outdoors using systems and devices that provide the same or greater level of operational safeguards that are available inside a nuclear power plant structure that is fully certifiable for indoor transfer.